In view of their potential danger as environmental pollutants, and understanding of the mechanism(s) of heavy metal detoxification in biological systems is imperative. Metallothionein is particularly well adapted for its role in detoxification since it is a small cysteinerich protein (20/61 residues) lacking aromatic or histidine residues. It has an unusually high affinity for transition metals. We have demonstrated that the metallothionein-I (MT-I) gene is transcriptionally regulated by Cd2 in CHO cells. Exposure of a subclone of these cells, R4OF, to 200 M Cd++ results in a 200X increase in MT-I protein, and an 80X increase in MT-I mRNA. The R4OF cells dsemonstrate gene amplification of 60-70X. When compared to several other systems, the R4OF cell offers several advantages in the study of eukaryotic gene regulation: 1) the amplified metallothionein genes provide a rich source for the isolation of the metallothionein product and hopefully, regulatory factors; 2) the gene is well defined with two introns and three exons, and the amplified gene appears to be confined to the long arm of a single large chromosome; 3) the amplified gene has a long half life even in the absence of inducer; 4) the cDNA probe for the gene is available; and 5) Cd++ provides a sensitive rapid reversible inducer of MT-I hnRNA synthesis. The present studies are directed to determine the conditions required for gene amplification of MT-II presumed to be glucocorticoid responsive. This will permit us to evaluate the gene regulation of both MT-I and MT-II hnRNA synthesis at the level of the nucleosome using DNase I sensitivity to identify active regions of chromatin in Cd++ and steroid induced gene activation; endonuclease release of HMG 14/17 proteins, acetylated histones, histone H3-exposed -SH and methylated DNA; and examine in vitro hnRNA transcripts from Cd++ induced systems treated with both our purified nuclear acetyltransferases (7,700) and our partially purified deacetylase.